Looking for help with system brainstorming

Ethan Brush · March 2015

I am going to be expanding my system quite a bit this summer and I am still brainstorming on a few broad details, just looking for some comments or suggestions on a few things. Basic outline is I will have about 6KW of PV, 1 KW of wind, 4K inverter. I have a 12/24 volt fridge, and will have radiant heat and I can get 12/24 volt circulators. Those two items I want to run directly off the batteries, but everything else will be 120AC. Mostly just small AC loads such as led lights, computer, speakers but will use big loads such as washer and power tools when sun is shining. The system will be "over paneled" quite it bit for my needs and battery bank because I want to heat water and maybe in the future use a small mini split when the sun is shining - diversion/opportunity. So what I am unsettled on is system voltage, 24 or 48, and whether to have 2 inverters or not. 24V has the advantage that I Can run my two DC things without a converter/battery equalizer, but if I decide to do DC diversion 6-7KW at 24 volts is a hassle. I may very well divert with the inverter (classic, SSR, etc) so maybe that is not that big a concern. 48 has the advantage (besides the usual obvious ones) that it is in the realm of doing DC diversion for 6-7 KW (I Actually already have a bunch of DC elements and several tristars), but I would need a DC converter or battery equalizer for my 2 DC things. One intriguing potential advantage of the 48 volt system is I could choose a 12 volt "sub system" for my DC stuff and then I could also use a morningstar suresin 300 for most of my AC loads which would lower inverter losses quite a bit, although not sure how much tare/standby losses one of those solar converter equalizer has, anyone know? Maybe the 2 inverter idea is not worth it, but another advantage of that would be I could use the big inverter for diversion and with the lights on the sure sine I wouldnt get the flicker that people have talked about when PWMing the inverter output.

So thats what I have so far. Any comments/ideas are appreciated. Oh one more thing, I have a 2 year old 24v battery bank (4 trojan l-16 RE

so going to 48 would require a new bank which is kinda a bummer but really in the scheme of things and considering its a small bank, not a deal breaker in the system voltage decision.

gww1 · March 2015

Since you said any comment welcome and also thanks again for walking me through my generator grounding issue. Here goes, I have no experiance with any other real system except outbacks 48 volt dual inverter one. I have almost my whole house on it which means at times some really big loads at one time. I have seen it carry 6000 watts at one time while watching it. I get some small flicker of lights sometimes when a 2000 watt load first starts. My belief is that I could add another 2000 watts solar panel with out buying more charge controllers and such.

The thing I like about 48 volt is you can do massive amounts of solar with the same equiptment that at 24 volts you would be stopped.

It seems like it is more flexable if you have to add anything except batteries. Again, remember I have no experiance with anything else, so keep this in mind when reading my comments. I am no expert.
Good luck
gww
PS on the light flicker when my opertunitie load kicks on and off through the cc. I know it sounds stupid but I kind of like the flicker. I can be in the house and know by the flicker when the battery is getting to absorb and when the flicker stops has reached absorb and if the flicker starts again that the sky has clouded up and I am barely carrying my loads again. I find these items midigate the fact that there is any flicker at all.

Photowhit · March 2015

You will have to have a diversion load and a dedicated charge controller for the wind, not sure if that makes wind less viable. I can't picture a setup where this diversion load wouldn't have to be different from your opportunity loads as it must be continuous, a water heater element in a small tank won't work, perhaps a heating element outside that can be drawn on when needed for hot air...

I personally would, and did, grow my system slowly. If you're not wanting to replace your battery bank, I would install 2-3kw of array now or even all of it and only use half now with your existing battery bank, make it switchable so you could use it all on cloudy days or just limit the output, severely, for your existing battery bank. 13-15% of current into the 350 amp hour 24v battery bank would be around 50 amps so you might be a bit limited on your opportunity loads until you replace you bank in 3-5 years. I say install it all, so you can take advantage of the tax credit which might be repealed after 2016.

I have a 4kw array and a 800ah 24 volt battery bank, and wish I had gone with a 48 volt, but I had purchased the battery for a somewhat smaller system. I run a small window unit around the clock in the summer time, and might add a mini split as an opportunity load as well if I get all things squared away. I also heat water 7 months out of the year (well year round, but 7 months that I can count on) but I'm a single guy so there isn't a huge demand on the water heater. I also have another 2600 watts of panel to install, but I am already over paneled. I suspect I will put them up over the new front porch this year, but time will tell, I think this is the 3rd year I had these good intentions...lol.

location plays a part, not sure where you are, in Mid Missouri our heat comes with the sun, so A/C is not a huge problem with a good sized system. I suspect with the extra panels and proper management I could do the whole 16x60 Tin Can (mobile home) all summer, I know I could do the bedroom all summer and the main room during the day time.

Good luck!

westbranch · March 2015

I chose 24V mainly because of the really high Voc and winter Vmp a 48 V system would create. Hi DC Voltage scares me, plus the added costs for equipment and the fact that I am right on the usage/power needs cusp between 24 and 48 volt.

Ethan Brush · March 2015

gww1 wrote: »

also thanks again for walking me through my generator grounding issue.

no problem! Did you get it hooked up?

You will have to have a diversion load and a dedicated charge controller for the wind, not sure if that makes wind less viable. I can't picture a setup where this diversion load wouldn't have to be different from your opportunity loads as it must be continuous, a water heater element in a small tank won't work, perhaps a heating element outside that can be drawn on when needed for hot air...

I dont see any reason that the "diversion" and "opportunity" cant be controlled together..... Unless I am missing something, here is what I envision: Setting the solar CC setpoints high so all it functions as is a MPPT DC-DC converter. Wind connects directly to batts (or connects to classic with safety shorting relay and its charging setpoints also set high), tristars are the charge controllers and divert off batteries to water tank. Your concern must be that the tank can always accept diverted/opportunity energy, but that will always be the case because the tank is very large or there is a "dump" circulator, etc....

location plays a part, not sure where you are, in Mid Missouri our heat comes with the sun, so A/C is not a huge problem with a good sized system. I suspect with the extra panels and proper management I could do the whole 16x60 Tin Can (mobile home) all summer, I know I could do the bedroom all summer and the main room during the day time.

Yeah Im in central NY. I hardly use any hot water in the summer as I prefer to mostly bathe in my creek, so it I'll likley be air conditioning rather that heating water for 4 months.

I chose 24V mainly because of the really high Voc and winter Vmp a 48 V system would create. Hi DC Voltage scares me, plus the added costs for equipment and the fact that I am right on the usage/power needs cusp between 24 and 48 volt.

Yeah you woulnt like working on my system then. 600VDC PV output! (more like 380 MPPT most of the time). Fortunately im an electrician by trade so that doesnt bother me

I think I am leaning (but not convinced!) toward the 48V with a 12V sub system. 12 volt is kinda handy to have available for other funky things I might do in the future - controls, relays, laptop, maybe a car stereo......48 would be much easier to divert CC with if I went the DC diversion route. The dc-dc converter or battery equalizer to make the 12 is another expense and phantom load though... I guess nothing is perfect.....

gww1 · March 2015

eithan

no problem! Did you get it hooked up?

Yes

I go thruogh the inverter for my opertunity load. I really like it but that is also why the lights flicker. Some loses but much smaller wire. Also running a bit of a distance, it only takes a very small sence wire from the cc and the water heater can use exsiting wire or be run from your critical load breaker panel. Not saying it is better, just saying my reasons it was simpler for me.
gww

Ethan Brush · March 2015

gww1 wrote: »

eithan

Yes

I go thruogh the inverter for my opertunity load. I really like it but that is also why the lights flicker. Some loses but much smaller wire. Also running a bit of a distance, it only takes a very small sence wire from the cc and the water heater can use exsiting wire or be run from your critical load breaker panel. Not saying it is better, just saying my reasons it was simpler for me.
gww

gww,

give me quick refresher on how yours is set up. Does you FM80 control an SSR? IF so, does the FM80 have the PWM option like the classic does?

gww1 · March 2015

ethan
I also so like it cause the element for the hot water heater can be got at the big box stores so easy to maintain. Yes, the fm80 puts out a 12 volt, small amp signal that I believe is pmw. I control a ssr with it. The ssr just breaks one wire of the 240 volt going to the hot water heater. My hot water heater is a 50 gal with 2000 watt elements in it. You could go 1500 watts or higher then 2000 watts. It is set up to preheat the water before it goes to my propane water heater. Chris olsen took time to explain it to me on the feildlines forum.

http://www.fieldlines.com/index.php/topic,147132.0.html

Good luck
gww

Looking for help with system brainstorming

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